This invention relates to unagglomerated metal oxide particles and methods for their production. More particularly, this invention relates to methods for the production of metal oxide particles by drying and thermal decomposition of chelated solutions of oxygen containing metal salts.
The uses for metal oxide particles are numerous and varied, ranging from active ingredients in antiperspirants to ceramic raw materials. In a vast majority of these applications, the size, shape, and density of the particles which make up the powder are of critical importance. The effects of one aspect of particle morphology, the particle size distribution, on sintering behavior and the properties of the final ceramic articles are well known. For example, substantially unagglomerated metal oxide particles of a relatively uniform particle size tend to sinter at low temperatures, saving time and energy in the production of ceramic articles based thereon. In addition, particles of this type tend to pack into a highly dense green body with uniform pore structure during processing, thus leading to a highly-dense, pore-free sintered body with uniform microstructure. Uniform particle size is also helpful in the prevention of localized exaggerated grain growth which may cause flaws and thereby adversely affect strength and other desirable properties of ceramic articles.
In some applications, it is highly desirable to produce multicomponent metal oxide particles having the characteristics mentioned above. For example, many ceramic articles of zirconium oxide (zirconia) are stabilized when doped with a relatively small fraction of a second metal oxide. In particular, it is known that zirconia has three allotropes: monoclinic, tetragonal, and cubic. A transition between the monoclinic and the tetragonal phases occurs at about 1200.degree. C. and involves a disruptive 4% change in volume. Because of this sharp volume change, "pure" or "unstabilized" zirconia is not generally useful for articles exposed to temperature fluctuations through the range at which the transformation occurs. It is known, however, that zirconia can be "wholly" or "partially" stabilized against this crystalline phase change by doping with such oxides as magnesium oxide, calcium oxide, and yttrium oxide. Such multiphase, stabilized materials, particularly the partially stabilized zirconias, have useful mechanical properties over a wide temperature range. It is important in making materials of this type that the stabilizing oxide be homogeneously dispersed throughout the ceramic article. Accordingly, a process for the production of multi-component metal oxide powders of homogeneous component distribution and in narrow particle-size ranges is highly desirable.